This invention generally relates to orthotic devices for controlling instabilities in joints, and is specifically concerned with an improved knee orthosis for correcting knee instabilities through a lightweight, compact mechanism which allows complete freedom of movement.
Orthotic devices for correcting knee instabilities are known in the prior art. Such devices are typically comprised of a mechanical joint that is supported by a pair of bracing members. The mechanical joint is formed from a pair of sidebars, each of which has a hinge-like pivoting joint in its middle portion. The top and bottom ends of the sidebars are connected to the bracing members. The bracing members fit around the regions of the leg above and below the kneejoint, and support the pivoting joints of the sidebars in alignment with the kneejoint so that the knee and the sidebars can pivot together as the wearer flexes his leg. Such prior art devices generally operate by confining the movement of the kneejoint as it bends so that unwanted motions of the lower femur and the upper tibia are eliminated or at least minimized.
Knee instabilities can take a variety of forms, including varus, valgus, rotary, anterior and posterior displacements, as well as hyperextension of the joint. Varus-type instabilities tend to bend the kneejoint outwardly, giving the leg a bow-legged orientation, while valgus instabilities tend to bend the kneejo:nt inwardly, giving the leg a knock-knee appearance. Rotary instabilities can cause the femural and tibial sections of the knee to rotate excessively with respect to one another as the knee flexes. Anterior instabilities tend to displace the tibia anteriorly with respect to the femur, while posterior instabilities tend to displace the tibia posteriorly as the knee flexes. Hyperextension-type instabilities allow the kneejoint to bend backward over 180.degree..
A properly installed orthotic knee brace can counteract all of these instabilities (at least in part) by reinforcing the kneejoint as a whole, and by supporting and guiding the lower femur and upper tibia as the kneejoint is flexed. Such devices are often needed by athletes competing in any running sport (such as football, hockey, tennis, etc.) who have suffered injuries to either the ligaments that interconnect the low er femur and upper tibia, or to the bones themselves, which make their joints much more prone to such unstable movements. For athletic applications, the ideal orthotic device would be capable of eliminating all such unstable movements through a mechanism that was extremely small and lightweight. Such a device would not diminish the speed or agility of the athlete to any significant extent, could be easily enclosed within a uniform, and would not rub against the other leg of the athlete when he was running.
Unfortunately, no such orthosis exists in the prior art that is capable of completely eliminating all such instabilities through a mechanical structure that is as lightweight and as compact as desired. The applicant believes that there are general reasons why the prior art has failed to develop an "ideal" knee orthosis. First, applicant is not aware of any prior art knee orthoses that are capable of applying a dynamic laterally directed stabilizing force to at least the inner condylar region as the knee flexes without impeding the motion of the knee. Hence, a "slack" exists in many prior art knee orthoses that allow s at least one of the previously discussed instabilities to occur to a significant degree. Secondly, the applicant has observed that not all of the aforementioned knee instabilities are equally common or equally debilitating, and that of all these instabilities, anterior tibial displacements are the most common and debilitating. Accordingly, control of anterior tibial displacements appears to be the key to controlling an unstable knee. Yet many prior art knee orthoses are not designed with any sort of priority in mind; instead, they allocate substantially the same amount of structure for each type of instability in an attempt to correct all instabilities simultaneously without regard for the fact that some types of instabilities are more common and debilitating than others. This lack of structural emphasis tends to make many prior art orthoses relatively heavy and bulky.
Clearly, there is a need for an improved knee orthosis that is capable of correcting all unwanted motions of an injured knee through a structure which concentrates on correcting the most common and debilitating knee instabilities in order to streamline the structure as much as possible. Ideally, such a mechanism should be simple, easy to construct and fit onto the knee of an athlete, and should resist slippage during vigorous athletic activity.